1. Field of the Invention
The present invention relates to measuring devices, more particularly, to spirit levels for determining if a work piece is at the desired angle.
2. Description of the Related Art
Spirit levels are old and well-known and enjoy wide usage. In general, a spirit level comprises an elongated frame with at least one flat reference surface and at least one spirit vial mounted in the frame. The vial contains a liquid with an entrapped bubble. The reference surface is placed against a workpiece and, when the bubble is centered between a pair of markings on the vial, that is, the vial is horizontal, that workpiece is known to be at a predetermined angle. Many spirit levels are provided with two or more vials at different fixed angles so that they can be used to check more than one surface angle. Naturally, as more vials are added, the level becomes more elongated and less portable.
One solution to the increased size of the multiple-angle spirit level, disclosed in U.S. Pat. No. 2,568,143, is the use of a single vial that has multiple surfaces for centering the bubble at different angles to a single reference surface. Another solution, disclosed in U.S. Pat. No. 5,127,16, uses a single vial with changeable end caps. The relative size of the two end caps determine the angle to be checked. Another solution, disclosed in numerous patents, is the adjustable level where the vial is mounted so that it can be rotated relative to the reference surface. The rotatable vial has an angular scale so that the angle of the vial to the reference surface can be set as desired.